I know zilch about these things so please keep it as basic as possible. I bought a 50W room air filter for my bedroom and would like to use it in the MH, as well, even when dry camping using my little 100W inverter. Question: How many amp-hours will it use to run it, say, for seven hours at night? Thank you.
Yep. What the last poster said. You can't/shouldn't drain the battery to less than 50% of full capacity. So if it is fully charged before you use it (fully means 100%, not 90%, stupid green light on panel is not too accurate), and air filter is the ONLY thing that this battery is used for, then it draws 40 Ah in 7 hours (inverter needs some juice for itself) and you need 80 Ah battery. Better make it 90 Ah. Again, this is if there is NOTHING else running off this battery, just air filter.
Not sure if you are making a statement or asking a question Piano fish, but if it's a question the answer is yes. It does, and a slight bit more. (just to play safe) plus the O/P said "keep it easy" and not much is easier than divide by 10.